Electrochromic nickel oxide simultaneously doped with lithium and a metal dopant

ABSTRACT

An electrochromic device comprising a counter electrode layer comprised of lithium metal oxide which provides a high transmission in the fully intercalated state and which is capable of long-term stability, is disclosed. Methods of making an electrochromic device comprising such a counter electrode are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/479,942, filed on Apr. 5, 2017, entitled “ELECTROCHROMIC NICKEL OXIDESIMULTANEOUSLY DOPED WITH LITHIUM AND A METAL DOPANT,” by Dane T.Gillaspie et al., which is a continuation of U.S. patent applicationSer. No. 14/031,573, filed on Sep. 19, 2013, entitled “ELECTROCHROMICNICKEL OXIDE SIMULTANEOUSLY DOPED WITH LITHIUM AND A META L. DOPANT,” byDane T. Gillaspie et al., now U.S. Pat. No. 9,651,845, which is acontinuation of U.S. patent application Ser. No. 13/554,144, filed onJul. 20, 2012, entitled “ELECTROCHROMIC NICKEL OXIDE SIMULTANEOUSLYDOPED WITH LITHIUM AND A METAL DOPANT,” by Dane T. Gillaspie et al., nowU.S. Pat. No. 8,687,261, which claims the benefit of the filing date ofU.S. Provisional Patent Application No. 61/510,381, filed Jul. 21, 2011,the disclosures of which are hereby incorporated herein by reference.

CONTRACTUAL ORIGIN

The United States Government has rights in this invention under ContractNo. DE-AC36-08G028308 between the United States Department of Energy andthe Alliance for Sustainable Energy, LLC, the Manager and Operator ofthe National Renewable Energy Laboratory.

BACKGROUND

Certain materials, referred to as electrochromic materials, are known tochange their optical properties in response to the application of anelectrical potential. This property has been taken advantage of toproduce electrochromic devices which can be controlled to transmitoptical energy selectively.

A number of factors affect the operation of an electrochromic device.One limitation on how dark an electrochromic device can become is howmuch charge can be stored in the counter electrode layer. In thiscontext, the term, “charge,” refers to the amount of electronic charge,or quantity of electrons per unit area, and the equivalent,corresponding quantity of charge balancing lithium ions per unit area,which may be conveniently expressed in units of milliCoulombs per squarecentimeter (mC/cm²). There have been many different approaches forproducing a charge storage medium, but most attention has focused on athin film deposited parallel to the electrochromic material layer, andseparated by an ionically conductive layer.

To date, most counter electrode layers have been made using NiO, LiNiO,or doped variants thereof. One advantage of using NiO and LiNiOmaterials is that under careful preparation conditions, the counterelectrode can be made so that it displays anodic electrochromism withgood electrochromic efficiency and a high bleached state lighttransmission. Here, the term, “electrochromic efficiency” refers to themodulation of optical density per amount of charge transferred per unitarea. Unfortunately, it has been difficult to intercalate lithium intoNiO based materials as a result of the material's compact crystallinestructure. As such, higher voltages must be applied to such materials tointercalate lithium, in order to drive the electrochromic response at areasonably fast rate, which leads to undesirable side reactions.

Other methods employ protons, or hydrogen ions instead of lithium ions,as the charge balancing counter ion for the coloration mechanism. Thesemethods may use counter electrode layers comprised of nickel hydroxides,or iridium oxides and other mixtures containing iridium. Typically anaqueous medium is also required to provide a suitable source of protons.Although it may be relatively easy to manufacture a counter electrodelayer capable of coloring anodically in an aqueous medium, it isdifficult to produce a complete device capable of long-term stability.It is, therefore, more advantageous to use lithium intercalation basedsystems.

A typical material used for counter electrode applications with lithiumis vanadium oxide, which is a material that forms crystal structuressimilar to those seen in tungsten oxide systems. The open crystallinelattice of vanadium oxide allows lithium intercalation more readily thanin NiO based structures. However, the presence of vanadium ions leads tothe generation of a strong yellow color. This yellow color is onlyslightly modulated by lithium intercalation, and shows a reasonablecathodic electrochromic effect throughout the majority of the visibleregion, thus limiting the maximum transmission that can be achievedusing this material as a counter electrode layer. Attempts to reduce thedegree of coloration by doping vanadium oxides with other componentsresult in a reduced electrochromic efficiency by reduction of the chargecapacity of the counter electrode layer. Such doping results in a devicewith a higher bleached state transmission at the cost of decreased rangeof modulation of optical density.

There remains a need for improved electrochromic coatings, and inparticular electrochromic coatings that comprise solid state, inorganicthin films, and metal oxide or metal oxide-containing thin films.

The foregoing examples of the related art and limitations relatedtherewith are intended to be illustrative and not exclusive. Otherlimitations of the related art will become apparent to those of skill inthe art upon a reading of the specification and a study of the drawings.

BRIEF SUMMARY OF THE INVENTION

The following embodiments and aspects thereof are described andillustrated in conjunction with systems, tools and methods that aremeant to be exemplary and illustrative, not limiting in scope. Invarious embodiments, one or more of the above-described problems havebeen reduced or eliminated, while other embodiments are directed toother improvements.

Exemplary embodiments describe an electrochromic device comprising acounter electrode comprised of a mixed oxide. In some embodiments, theelectrochromic device is comprised of five sequential layers includingtwo conductive layers, an electrochromic layer, an ion conductor layer,and a counter electrode layer.

An embodiment, by way of non-limiting examples, includes anelectrochromic device comprising: (a) a first electrode comprising oneof an electrochromic layer or a counter electrode layer, (b) a secondelectrode comprising the other of the electrochromic layer or thecounter electrode layer, (c) an ion-conductor layer for conducting ionsbetween the first and second electrodes, (d) a first conductive layer,and (e) a second conductive layer, the first and second electrodes andthe ion-conductor layer being sandwiched between the first and secondconductive layers, the counter electrode layer comprising at least onemixed oxide having a formula Li_(x)Ni(II)_(1-y)Ni(III)_(y)M_(z)O_(a),where M is a metal, and x is about 0 to about 10, y is about 0 to about1, z is about 0 to about 10, and a is from about (0.5x+1+0.5y+z) toabout (0.5x+1+0.5y+3.5z).

In some embodiments, the mixed oxide has the formulaLi_(x)Ni(II)_((1-y))Ni(III)_((y))M(A)_(z)O_((1+0.5x+0.5y+1.5z)), where Ais the oxidation state of the metal M. In some embodiments, M(A) isselected from the group consisting of Al(III), Sc(III), Cr(III),Co(III), Y(III), Rh(III), In(III), La(III), Ce(III), Nd(III), andSc(III).

In some embodiments, the mixed oxide has the formulaLi_(x)Ni(II)_((1-y))Ni(III)_((y))M(A)_(z)O_((1+0.5x+0.5y+2z)), where Ais the oxidation state of the metal M. In some embodiments, M(A) isselected from the group consisting of Si(IV), Ti(IV), Mn(IV), Zr(IV),Sn(IV), Ce(IV), Hf(IV), Re(IV), and Ir(IV).

In some embodiments, the mixed oxide has the formulaLi_(x)Ni(II)_((1-y))Ni(III)_((y))M(A)_(z)O_((1+0.5x+0.5y+2.5z)), where Ais the oxidation state of the metal M. In some embodiments, M(A) isselected from the group consisting of V(V), Nb(V), Sb(V), Ta(V), andPa(V).

In some embodiments, the mixed oxide has the formulaLi_(x)Ni(II)_((1-y))Ni(III)_((y))M(A)_(z)O_((1+0.5x+0.5y+3z)), where Ais the oxidation state of the metal M. In some embodiments, M(A) isselected from the group consisting of Cr(VI), Se(VI), Mo(VI), Te(VI),and W(VI).

In some embodiments, the mixed oxide isLi_(2.3)Ni(II)_((0.5))Ni(III)_((0.5))Y(III)_(0.3)O_(a), where a is asdefined herein. In some embodiments, the mixed oxide isLi_(2.3)Ni(II)_((0.5))Ni(III)_((0.5))Y(III)_(0.3)O_(3.1).

In some embodiments, the mixed oxide isLi_(2.3)Ni(II)_((0.5))Ni(III)_((0.5))Zr(IV)_(0.3)O_(a), where a is asdefined herein. In some embodiments, the mixed oxide isLi_(2.3)Ni(II)_((0.5))Ni(III)_((0.5))Zr(IV)_(0.3)O_(3.25).

In some embodiments, the mixed oxide isLi_(2.3)Ni(II)_((0.5))Ni(III)_((0.5))Hf(IV)_(0.3)O_(a), where a is asdefined herein. In some embodiments, the mixed oxide isLi_(2.3)Ni(II)_((0.5))Ni(III)_((0.5))Hf(IV)_(0.3)O_(3.25).

In some embodiments, the mixed oxide isLi_(2.3)Ni(II)_((0.5))Ni(III)_((0.5))Zr(IV)_(0.294)Hf(IV)_(0.006)O_(a),where a is as defined herein. In some embodiments, the mixed oxide isLi_(2.3)Ni(II)_((0.5))Ni(III)_((0.5))Zr(IV)_(0.294)Hf(IV)_(0.006)O_(3.25),where it is believed that the final composition reflects about thelevels of hafnium impurity normally encountered in commerciallyavailable grades of zirconium starting materials.

In some embodiments, the mixed oxide isLi_(2.3)Ni(II)_((0.5))Ni(III)_((0.5))Ta(V)_(0.3)O_(a), where a is asdefined herein. In some embodiments, the mixed oxide isLi_(2.3)Ni(II)_((0.5))Ni(III)_((0.5))Ta(V)_(0.3)O_(3.4).

In some embodiments, the mixed oxide is further doped with an additionalmetal or metal oxide. In some embodiments, the mixed oxide has anoptical density in the dark state of at least about 10 μm⁻¹ at anoptical wavelength of about 450 nm. In some embodiments, the mixed oxidehas a bleached state optical absorption of less than about 0.5 μm⁻¹ atan optical wavelength of about 450 nm. In some embodiments, the mixedoxide has a refractive index of at least about 2.0. In some embodiments,the thickness of the counter electrode layer ranges from about 80 nm toabout 500 nm. In some embodiments, the thickness ranges from about 100nm to about 320 nm. In some embodiments, the mixed oxide issubstantially amorphous. In some embodiments, the mixed oxide isprepared by reactive sputter deposition. In some embodiments, the mixedoxide is prepared by d.c. magnetron reactive sputter deposition. In someembodiments, the electrochromic device is incorporated into an insulatedglazing unit.

Another non-limiting embodiment includes an insulated glazing unitcomprising an electrochromic device as described herein and anotherglass panel separated from the electrochromic device.

Another non-limiting embodiment includes a method for depositing a mixedoxide disclosed herein onto a substrate by means of reactive sputteringdeposition, where the substrate may be glass, plastic, a laminate, anelectrochromic device, a thin film, or a metal.

Another non-limiting embodiment includes a method for the preparation ofan electrochromic device comprising: (a) providing a first conductivelayer, (b) depositing one of an electrochromic layer or a counterelectrode layer on the first conductive layer, thereby providing a firstdeposited electrode, (c) depositing an ion-conductor layer on the firstdeposited electrode, (d) depositing the other of the electrochromiclayer or the counter electrode layer on the ion-conductor layer, therebyproviding a second deposited electrode, (e) depositing a secondconductive layer on the second deposited electrode, wherein the counterelectrode layer comprises a mixed oxide having a formulaLi_(x)Ni(II)_(1-y)Ni(III)_(y)M_(z)O_(a), where M is a metal, and x isabout 0 to about 10, y is about 0 to about 1, z is about 0 to about 10,and a is from about (0.5x+1+0.5y+z) to about (0.5x+1+0.5y+3.5z). In someembodiments, the method further comprises depositing lithium into one ofthe ion-conductor layer or the counter electrode layer.

In some embodiments, the mixed oxide has the formulaLi_(x)Ni(II)_((1-y))Ni(III)_((y))M(A)_(z)O_((1+0.5x+0.5y+1.5z)), where Ais the oxidation state of the metal M. In some embodiments, M(A) isselected from the group consisting of Al(III), Sc(III), Cr(III),Co(III), Y(III), Rh(III), In(III), La(III), Ce(III), Nd(III), andSc(III). In some embodiments, the mixed oxide has the formulaLi_(x)Ni(II)_((1-y))Ni(III)_((y))M(A)_(z)O_((1+0.5x+0.5y+2z)), where Ais the oxidation state of the metal M. In some embodiments, M(A) isselected from the group consisting of Si(IV), Ti(IV), Mn(IV), Zr(IV),Sn(IV), Ce(IV), Hf(IV), Re(IV), and Ir(IV). In some embodiments, themixed oxide has the formulaLi_(x)Ni(II)_((1-y))Ni(III)_((y))M(A)_(z)O_((1+0.5x+0.5y+2.5z)), where Ais the oxidation state of the metal M. In some embodiments, M(A) isselected from the group consisting of V(V), Nb(V), Sb(V), Ta(V), andPa(V). In some embodiments, the mixed oxide has the formulaLi_(x)Ni(II)_((1-y))Ni(III)_((y))M(A)_(z)O_((1+0.5x+0.5y+3z)), where Ais the oxidation state of the metal M. In some embodiments, M(A) isselected from the group consisting of Cr(VI), Se(VI), Mo(VI), Te(VI),and W(VI). In some embodiments, the counter electrode is deposited byd.c. magnetron reactive sputtering.

Another non-limiting embodiment includes an electrochromic devicecomprising: (a) a first electrode comprising one of an electrochromiclayer or a counter electrode layer, (b) a second electrode comprisingthe other of the electrochromic layer or the counter electrode layer,(c) an ion-conductor layer for conducting ions between the first andsecond electrodes, (d) a first conductive layer, and (e) a secondconductive layer, the first and second electrodes and the ion-conductorlayer being sandwiched between the first and second conductive layers,the counter electrode layer comprising at least one mixed oxide having aformula Li_(x)Ni(II)_(1-y)(III)_(y)M_(z)O_(a), where M is a metal, and xis about 0 to about 10, y is about 0 to about 1, z is about 0 to about10, and a is about 0 to about 10.

In addition to the aspects and embodiments described above, furtheraspects and embodiments will become apparent by reference to thedrawings and by study of the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are illustrated in referenced figures of thedrawings. It is intended that the embodiments and figures disclosedherein are to be considered illustrative rather than limiting.

FIG. 1 shows an external circuit driving electrons from a counterelectrode (CE) to an electrochromic layer (EC) via the outer transparentconductors (TC).

FIGS. 2 a-2 c illustrate the structure of a counterelectrode layer.

FIG. 3 illustrates the soft X-ray absorption spectrum for various mixednickel oxide materials.

FIG. 4 illustrates the result of treating nickel oxide materials withozone.

FIG. 5 a is a scanning electron micrograph of a fracture edge of aLi_(1.81)NiW_(0.21)O_(x) material.

FIG. 5 b illustrates the x-ray diffraction pattern for aLi_(1.81)NiW_(0.21)O_(x) material.

FIG. 6 compares the soft X-ray absorption spectrum forLi_(1.81)NiW_(0.21)O_(x) material with other mixed nickel oxides.

FIG. 7 a compares cyclic voltammograms and corresponding 670 nm lighttransmission signals for 80 nm thick, 1 cm² samples ofLi_(2.34)NiZr_(0.28)O_(x).

FIG. 7 b compares cyclic voltammograms and corresponding 670 nm lighttransmission signals for 80 nm thick, 1 cm² samples ofLi_(1.81)NiW_(0.21) ⁰ _(x).

FIG. 7 c depicts the optical spectra for the as deposited, bleached anddark states corresponding to the cyclic voltammograms in FIGS. 7 a andb.

FIG. 7 d depicts a photograph of the Li_(2.34)NiZr_(0.28)O_(x) in thebleached and dark states, corresponding to the cyclic voltammogram andoptical transmission response in FIG. 7 a.

FIG. 8 shows the cyclic voltammogram and corresponding 670 nm lighttransmission through a Li_(2.34)NiZr_(0.28)O_(x) material.

FIGS. 9 a and 9 b depict the change in optical transmission for 670 nmlight, for bleaching from the fully dark state.

FIGS. 10 a-10 f depict X-ray Photoelectron Spectra (XPS) forLi_(2.34)NiZr_(0.28)O_(x) and Li_(1.81)NiW_(0.21)O_(x) materials.

FIG. 11 a provides a soft X-ray spectrum for Li_(2.34)NiZr_(0.28)O_(x)material.

FIG. 11 b depicts a structure for surface lithium peroxide formation ona layer of Li_(2.34)NiZr_(0.28)O_(x).

FIGS. 12 a-12 c depict cyclic voltammograms and correspondingtransmission signals for 670 nm light for NiZr_(x)O_(y) materials.

FIGS. 13 a and 13 b depict electrochromic switching results forLi_(x)NiO_(x) materials.

FIGS. 14 a and 14 b illustrate X-ray absorption spectra forLi_(2.34)NiZr_(0.28)O_(x) materials.

FIGS. 15 a and 15 b illustrate X-ray absorption spectra forLi_(1.81)NiW_(0.21)O_(x) materials.

FIG. 16 illustrates a trend in Ni(II)O nanocrystal size for certainmaterials.

DETAILED DESCRIPTION

Embodiments described herein provide an electrochromic device having acounter electrode, which provides a high transmission in the fullyintercalated state and is capable of long-term stability suitable foruse as a commercial product.

As used herein, the term “bleached state” means the state of anelectrochromic material that is at least partially clear or at leastpartially non-colored.

As used herein, the term “counter ion” means a mobile, transportable,positively charged ion such as H⁺ (proton) or Li⁺ (lithium ion.)

As used herein, the term “electrochromic efficiency” means the opticaldensity change per amount of charge transferred per unit area.

As used herein, the term “intercalation” means the reversible insertionof a molecule, atom or ion into a crystal lattice.

As used herein, the term “lithium” means elemental lithium, its salts,oxides, coordination complexes, and chelates. “Lithium” may also referto lithium ions.

As used herein, the term “optical density” of the dark or fully coloredstate means the natural logarithm of the bleached state opticaltransmission divided by the dark state transmission, at a givenwavelength, or over a specified wavelength range.

As used herein, the term “optical density” of the bleached state meansthe natural logarithm of 100% transmission divided by the bleached statetransmission, at a given wavelength, or over a specified wavelengthrange.

As used herein, the term “specific optical density” of a specified layermeans the optical density divided by the thickness of the layer.

As used herein, the term “sputtering” means a physical process wherebyatoms in a solid target material are ejected into the rarefied gasplasma phase due to bombardment of the material by energetic ions.“Sputtering” will be discussed with regard to its use in filmdeposition.

FIG. 1 shows a five-layer electrochromic device in cross-section. Insome embodiments, the device will have at least the following sequentiallayers: an electrochromic layer (“EC”) 30 which produces a change inabsorption or reflection upon oxidation or reduction; an ion conductorlayer (“IC”) 32 which serves as an electrolyte, allowing the passage ofions while blocking electronic current; a counter electrode (“CE”) 28which serves as a storage layer for ions when the device is in thebleached state; and two conductive layers (“CL”) 24 and 26 which serveto apply an electrical potential to the electrochromic device. Each ofthe aforementioned layers is applied sequentially on a substrate 34.

A low voltage electrical source 22 is connected to the device by meansof conductive wires. In order to alter the optical properties of window20, in some embodiments an electrical potential can be applied acrossthe layered structure. The polarity of the electrical source will governthe nature of the electrical potential created and, thus, the directionof ion and electron flow. The electrical potential created will causeions to flow from the counter electrode layer 28 through the ionconductor layer 32 to the electrochromic layer 30, thereby causing theelectrochromic layer 30 to transform to the colored state therebycausing the transparency of the window 20 to be reduced.

The materials employed for the conductive layers 24 and are well knownto those skilled in the art. Exemplary conductive layer materialsinclude coatings of indium oxide, indium tin oxide, doped indium oxide,tin oxide, doped tin oxide, zinc oxide, doped zinc oxide, rutheniumoxide, doped ruthenium oxide and the like, as well as all thin metalliccoatings that are substantially transparent, such as transition metalsincluding gold, silver, aluminum, nickel alloy, and the like. It is alsopossible to employ multiple layer coatings, such as those available fromPilkington under the tradename of TEC-Glass®, or those available fromPPG Industries under the tradenames SUNGATE® 300 and SUNGATE® 500. Theconductive layers 24 and 26 may also be composite conductors prepared byplacing highly conductive ceramic and metal wires or conductive layerpatterns on one of the faces of the substrate and then overcoating thiswith transparent conductive materials such as indium tin oxide or dopedtin oxides. The conductive layers may be further treated withappropriate anti-reflective or protective oxide or nitride layers.

In some embodiments, the material selected for use in conductive layer26 is the same as the material selected for use in conductive layer 24.In other embodiments, the material selected for use in conductive layer26 is different than the material selected for use in conductive layer24.

In some embodiments, the conductive layers utilized are transparentlayers of indium tin oxide. Typically, the conductive layer 26 isdisposed on a substrate having suitable optical, electrical, thermal,and mechanical properties such as, for example, glass, plastic or mirrormaterials, as a coating having a thickness in the range of about 5 nm toabout 10,000 nm, and preferably about 10 nm to about 1,000 nm. However,any thickness of the conductive layer may be employed that providesadequate conductance for the electrochromic device and which does notappreciably interfere with the transmission of light where required.Moreover, conductive layer 24 is typically the final layer of theelectrochromic device deposited on the counter electrode layer 28. Otherpassive layers used for improving optical properties, or providingmoisture or scratch resistance may be deposited on top of the activelayers. These conductive layers are connected to an electrical powersource in a conventional manner.

The electrochromic layer 30 (“EC layer” or “EC”) may be comprised ofmaterials including inorganic, organic blends and/or composites ofinorganic and organic electrochemically active materials such that theEC layer is capable of receiving ions transferred from the CE layer 28.Exemplary inorganic metal oxide electrochemically active materialsinclude WO₃, V₂O₅, MoO₃, Nb₂O₅, TiO₂, CuO, Ni₂O₃, Ir₂O₃, Cr₂O₃, Co₂O₃,Mn₂O₃, mixed oxides (e.g W—Mo oxide, W—V oxide) and the like. Oneskilled in the art would recognize that each of the aforementioned metaloxides might be appropriately doped with lithium, sodium, potassium,molybdenum, vanadium, titanium, and/or other suitable metals orcompounds containing metals. In a preferred embodiment, the EC layer 30is selected from WO₃ or doped WO₃.

The thickness of the EC layer 30 may vary depending on theelectrochemically active material chosen. However, the EC layer 30typically ranges from about 500 Angstroms to about 20,000 Angstroms inthickness, preferably from about 3400 Angstroms to about 5500 Angstroms.

Overlying the electrochromic layer 30 is an ion conductor layer 32. Theion conductor layer 32 is comprised of a solid electrolyte capable ofallowing ions to migrate through the layer. The ion conductor layer 32must have a sufficient ionic transport property to allow ions,preferably lithium ions, to migrate through. Any material may be usedfor an ion conductor provided it allows for the passage of ions from thecounter electrode layer 28 to the electrochromic layer 30. In someembodiments, the ion conductor layer comprises a silicate-basedstructure. In other embodiments, suitable ion conductors particularlyadapted for lithium ion transmission include, but are not limited to,lithium silicate, lithium aluminum silicate, lithium aluminum borate,lithium borate, lithium zirconium silicate, lithium niobate, lithiumborosilicate, lithium phosphosilicate, lithium nitride, lithium aluminumfluoride, and other such lithium-based ceramic materials, silicas, orsilicon oxides. Other suitable ion-conducting materials can be used,such as silicon dioxide or tantalum oxide, and a wide selection ofcomplex, garnet-like and/or perovskite-like materials based onlithium-lanthanide-transition metal oxides. The overall ion conductorlayer may be comprised of multiple component layers of alternating ordiffering materials, including reaction products between at least onepair of neighboring layers. In some embodiments, the refractive indexand thickness of the ion conductor layer are selected to maximize lighttransmission while minimizing electronic current. In some embodiments,the ion conductive layer 32 has low or no electronic conductivity. Insome embodiments, the combination of the ion conductor layer and itsmaterial interfaces with the neighboring counter electrode andelectrochromic layers serves to, it is believed, effectively block theflow of electronic current over the electrical potential range ofelectrochromic operation. The preferred ion conductor material is alithium-silicon-oxide produced by either sputtering or a sol-gelprocess.

The thickness of the IC layer 32 may vary depending on the material.However, the IC layer 32 typically ranges from about 100 Angstroms toabout 700 Angstroms in thickness, preferably from about 200 Angstroms toabout 600 Angstroms in thickness, and most preferably from about 325Angstroms to about 475 Angstroms in thickness.

The counter electrode layer 28 (“CE layer or “CE”) is capable of storinglithium and then releasing the lithium for transfer to theelectrochromic layer 30 in response to an appropriate electricalpotential. In some embodiments, the counter electrode is capable ofdarkening anodically, allowing the material to be used as acomplementary counter electrode for cathodically coloring electrochromicmaterials such as tungsten oxide.

In some embodiments, the counter electrode layer 28 comprises a materialhaving the general formula Li_(x)Ni_(y)M_(z)O_(a), where M is a metal,and x is about 0 to about 10, y is about 0 to about 1, z is about 0 toabout 10, and a is from about (0.5x+1+0.5y+z) to about(0.5x+1+0.5y+3.5z). The metal may be aluminum, scandium, chromium,yttrium, rhodium, indium, lanthanum, cerium, neodymium, samarium,zirconium, silicon, titanium, manganese, tin, hafnium, rhenium, iridium,vanadium, niobium, antimony, tantalum, protactinium, chromium, selenium,molybdenum, tellurium, tungsten, or uranium. Examples of materialsaccording to this formula include Li_(x)Ni_(y)Ta_(z)O_(a),Li_(x)Ni_(y)Nb_(z)O_(a), Li_(x)Ni_(y)Zr_(z)O_(a), andLi_(x)Ni_(y)Hf_(z)O_(a), and x is about 0 to about 10, y is about 0 toabout 1, z is about 0 to about 10, and a is from about (0.5x+1+0.5y+z)to about (0.5x+1+0.5y+3.5z).

In some embodiments, the CE material is selected such that is meets atleast one of the following: (a) an ionic charge or oxidation stategreater than or equal to +3; (b) oxide stability or formation energy(Gibbs free energy of formation) of the corresponding oxide greater thanor equal to about 500 kJ/mole; (c) electronegativity less than about 1.3on the Pauling scale; (d) an ionic radius less than or equal to about130 pm; (e) a band gap energy of a corresponding oxide greater thanabout 4 eV; (f) negligible optical absorption over about the visibleregion of the corresponding oxide; (g) an open crystal lattice or oxidestructure characterized by a lattice spacing greater than about 0.3 nm;(h) a relative insolubility of nickel oxide into the corresponding oxideup to temperatures of about 900K; (k) a lithium ion conductivity of thecorresponding lithium metal oxide of greater than about 1×10⁻⁹ Scm⁻².

In some embodiments, the CE material has the general formulaLi_(x)Ni(II)_((1-y))Ni(III)_((y))M(A)_(z)O_(a), where M is a metalrecited above; A is the most favorable oxidation state of the metal, M;B is 1, 1.5, 2, 2.5, or 3, depending on the oxidation state, A; and eachof x and z range from about 0 to about 10, y ranges from about 0 toabout 1, and a ranges from about 0 to about 10.

In some embodiments, the CE material has the general formulaLi_(x)Ni(II)_((1-y))Ni(III)_((y))M(A)_(z)O_((1+0.5x+0.5y+Bz)), where Mis a metal recited above; A is the most favorable oxidation state of themetal, M; B is 1, 1.5, 2, 2.5, or 3, depending on the oxidation state,A; and each of x and z range from 0 to 10, while y can range from 0to 1. In these embodiments, the sum (1+0.5x+0.5y+Bz) provides, it isbelieved, an estimate of the oxygen stoichiometry. The exactstoichiometric formula for the materials of the CE layer depend, it isbelieved, ultimately on the electrochromic state (darkened or bleached)since lithium moves into the material when the material switches fromdark to bleached. In general, however, it is believed that the materialsmay fall into a wide range of sub-stoichiometry throughsuper-stoichiometry for oxygen content. In some embodiments, the rangeof stoichiometry may vary as much as about 30%. As such, the oxidationstate A of metal species M is understood to be the primary oxidationstate of metal species, M, where one skilled in the art would appreciatethat minor proportions of other oxidation states may be present in thematerial. This is especially true for thermodynamically metastablematerials derived from sputter deposition and other high-energydeposition processes, materials involved in reversible electrochemicalprocesses, and materials of high internal interfacial surface area. Ingeneral for the stoichiometric formulae listed above, B=A/2. B denotesthe oxygen stoichiometry required to balance, account for, or neutralizethe “formal charge” or oxidation state, A, of metal species M, where“formal charge” on one oxygen atom is taken to be −2. For example, whenM(A)=Zr(IV), then M=Zr and the oxidation state, or formal charge, A,=+4.Here, two oxygen atoms, with a total formal charge of −4, are requiredto balance the formal charge, A,=+4.

In some embodiments, x ranges from about 1 to about 4; y ranges fromabout 0.1 to about 1; and z ranges from about 0.05 to about 2. In otherembodiments, x ranges from about 1.5 to about 3; y ranges from about 0.4to about 0.95; and z ranges from about 0.15 to about 1. In otherembodiments, x ranges from about 2 to about 2.5; y ranges from about 0.6to about 0.9; and z ranges from about 0.2 to about 0.5.

In some embodiments, A is II, III, IV, V, or VI. In other embodiments, Ais III, IV, or V. In yet other embodiments, A is IV.

In some embodiments, M is Mg(II), Y(III), La(III), Ce(III), Si(IV),Ti(IV), Zr(IV), Hf(IV), Ir(IV), Nb(V), Ta(V), Mo(VI), or W(VI). In otherembodiments, M is La(III), Ce(III), Zr(IV), Hf(IV), Nb(V), or Ta(V). Inyet other embodiments, M is Zr(IV) or Hf(IV).

In some embodiments, the CE material has the formulaLi_(x)Ni(II)_((1-y))Ni(III)_((y))M(A)_(z)O_((1+0.5x+0.5y+1.5z)), where Mis selected from the group consisting of Al(III), Sc(III), Cr(III),Co(III), Y(III), Rh(III), In(III), La(III), Ce(III), Nd(III), andSc(III).

In some embodiments, the CE material has the formulaLi_(x)Ni(II)_((1-y))Ni(III)_((y))M(A)_(z)O_((1+0.5x+0.5y+2z)), where Mis selected from the group consisting of (Si(IV), Ti(IV), Mn(IV),Zr(IV), Sn(IV), Ce(IV), Hf(IV), Re(IV), and Ir(IV).

In some embodiments, the CE material has the formulaLi_(x)Ni(II)_((1-y))Ni(III)_((y))M(A)_(z)O_((1+0.5x+0.5y+2.5z)), where Mis selected from the group consisting of V(V), Nb(V), Sb(V), Ta(V), andPa(V).

In some embodiments, the CE material has the formulaLi_(x)Ni(II)_((1-y))Ni(III)_((y))M(A)_(z)O_((1+0.5x+0.5y+3z)), where Mis selected from the group consisting of Cr(VI), Se(VI), Mo(VI), Te(VI),and W(VI).

In some embodiments, the material isLi_(2.3)Ni(II)_((0.5))Ni(III)_((0.5))Y(III)_(0.3)O_(3.1).

In some embodiments, the material isLi_(2.3)Ni(II)_((0.5))Ni(III)_((0.5))Zr(IV)_(0.3)O_(3.25).

In some embodiments, the material isLi_(2.3)Ni(II)_((0.5))Ni(III)_((0.5))Hf(IV)_(0.3)O_(3.25).

In some embodiments, the material isLi_(2.3)Ni(II)_((0.5))Ni(III)_((0.5))Zr(IV)_(0.294)Hf(IV)_(0.006)O_(3.25).

In some embodiments, the material isLi_(2.3)Ni(II)_((0.5))Ni(III)_((0.5))Ta(V)_(0.3)O_(3.4).

It is believed that the materials of the prior art change in opticaldensity (i.e. an increase in light absorption) over a wavelength rangethat extends from blue (about 450 nm to about 500 nm) throughultraviolet (less than about 430 nm), rendering transmitted sunlightbrown. This modulation in optical density is complementary to tungstenoxide (or any other material comprising the electrochromic layer), whichexhibits a reversible change in optical density primarily from red(about 640 nm) through the infrared wavelength range (greater than about740 nm), rendering transmitted light blue.

As compared with prior art mixed oxides, it is believed that the mixedoxides described herein have an increased light transmission in the bluewavelength region of the spectrum, especially when the mixed oxides usedin the CE layer are in the bleached state. As a result, it is believedthat these materials may be used to fabricate electrochromic devicesthat appear closer to “water white” in color, i.e. less yellow thanprior art electrochromic devices incorporating prior art CE materials.It is believed that this may be achieved without the aid of additionalcolor balancing filter media (although, filters and other opticalenhancement means may still be included in the electrochromic devices,or IGUs comprising the devices).

It is believed that when the mixed oxide CE materials described hereinare used in an electrochromic device as a complementary counterelectrode, with tungsten oxide used for the working electrode, thecombination of blue light absorption through the counter electrode andred light absorption through the tungsten oxide will yield anelectrochromic window coating that appears neutral grey when backlitwith sunlight, effectively functioning as a variable neutral densityfilter, with the transmitted light nearly white but at a lower intensitythan that of the incident light.

The CE materials described herein, in particularLi_(2.3)Ni(II)_(0.5)Ni(III)_(0.5)Zr_(0.29)O_(2.73), appear to either (1)bleach more completely, and/or (2) bleach more reversibly, than priorart CE materials. As a result, the materials exhibit higher levels oflight transmission in the bleached state, after attaining comparableoptical density levels for the dark state. Moreover, the bleached statetransmission does not appear to degrade with prolonged cycling betweendark and bleached states. In fact, it is believed that modifications tothe basic crystal structure and electronic state of the nanocrystallineNiO(II) material, resulting from doping by Zr(IV) and Li(I) ions, isbelieved to be responsible for the improved reversibility.

The specific optical density of the dark state, at an optical wavelengthof about 450 nm, of the mixed oxide CE materials disclosed herein, mayvary depending on the material chosen. However, the mixed oxide CEmaterials typically range from about 5 μm⁻¹ to about 20 μm⁻¹ in specificoptical density, in the dark state at about 450 nm, preferably fromabout 8 μm⁻¹ to about 12 μm⁻¹. In some embodiments, the mixed oxide CEmaterial has a specific optical density in the dark state of about 10μm⁻¹ at an optical wavelength of about 450 nm.

The specific optical density of the bleached state, at an opticalwavelength of about 450 nm, of the mixed oxide CE materials disclosedherein, may vary depending on the material chosen. However, the mixedoxide CE materials typically range from about 0.1 μm⁻¹ to about 1 μm⁻¹in specific optical density, in the bleached state, preferably from lessthan about 0.1 μm⁻¹ to about 0.5 μm⁻¹. In some embodiments, the mixedoxide CE materials disclosed herein have a specific optical density atabout 450 nm for the bleached state of less than about 0.5 μm⁻¹ at about450 nm. In other embodiments, the mixed oxide CE materials disclosedherein have a bleached state optical transmission from about 60% greaterthan about 99% at about 450 nm (assuming a CE layer thickness of about200 nm), and in some embodiments from about 75% to 99%.

In some embodiments, the mixed oxide CE materials disclosed herein havea mixed electronic and ionic conductivity from about 10⁻¹¹ Scm⁻¹ toabout 10⁻⁶ Scm⁻¹, preferably greater than about 10⁻¹⁰ Scm⁻¹. In someembodiments, the mixed oxide CE materials have a lithium charge capacityof about from about 10 mC/cm² to about 100 mC/cm² for a film about 160nm thick, depending on the chosen composition.

In some embodiments, the mixed oxide CE materials disclosed herein havea refractive index from about 1.7 to about 2.5, depending on the chosencomposition, to match the refractive indices of neighboring films of theEC stack.

In some embodiments, when the mixed oxide CE materials are incorporatedinto an electrochromic device, the electrochromic efficiency of thedevice can range from about 10 cm²/C to about 80 cm²/C at an opticalwavelength of about 450 nm, depending upon the materials chosen for theEC layer 30 and the CE layer 28, and their respective thicknesses.

In some embodiments, the materials selected for the CE layer generallyhave an optical band gap energy of at least about 3 eV. In otherembodiments, the materials selected for the CE layer generally have aband gap energy that can range from about 2.5 eV to about 6 eV,depending on the material chosen.

In some embodiments, at least about 50% of the nickel in the mixed oxideCE materials disclosed herein reside at the surface of the nanocrystals.In some embodiments, the NiO nanocrystals range in size from about 3 nmto about 12 nm. In other embodiments, the NiO nanocrystals range in sizefrom about 4 nm to about 10 nm. In yet other embodiments, the NiOnanocrystals range in size from about 5 nm to about 8 nm.

The thickness of the counter electrode layer 28 is variable depending onthe application sought for the electrochromic device and thetransmission range desired. As such, the thickness may range from about80 nm to about 500 nm. In some embodiments, the thickness ranges fromabout 100 nm to about 320 nm. In other embodiments, the thickness rangesfrom about 120 nm to about 240 nm. In some embodiments, these ranges mayscale inversely with the quotient y/(x+z).

The thickness of the counter electrode comprising the CE materials mayalso scale with the thickness of the tungsten oxide layer and thedesired optical density charge of the complete electrochromic coating.For a y/(x+z) value of 0.2 and a tungsten oxide thickness of about 500nm, or one preferred counter electrode thickness of 200 nm, thepreferred thickness can be expressed as: (2*d*y)/(x+z), where d is thethickness of the tungsten oxide layer in manometers.

For example, (2*500 nm*0.5)/(2.3+0.3)=192 nm. In other words, when thetungsten oxide layer is designed to be about 500 nm thick, to obtain adark state transmission level of less than about 1.5%, and an opticaldensity change of about 1.6, then the counter electrode layer comprisedof the CE material should be about 192 nm thick.

This quantity is believed to be proportional to the concentration of theprimary light absorbing species Ni(III). In some embodiments, the valuefor y/(x+z) is about 0.2. For higher concentrations of Ni(III), thelayer may need to be thinner, while for more dilute, smallerconcentrations, the layer may need to be thicker, to offer the samemodulation in optical density.

In some embodiments, the mixed oxide is present in an amorphous state.In other embodiments, the mixed oxide is present in a crystalline state.In yet other embodiments, the mixed lithium nickel metal oxide may bepresent in a mixed amorphous and crystalline state. For example, about50% of the material comprising the mixed oxide may be in an amorphousstate. Without wishing to be bound by any particular theory, in someembodiments, the mixed oxides are nano-composites or fine dispersions ofnanocrystals in an amorphous matrix. In some embodiments, and againwithout wishing to be bound by any particular theory, the mixed oxidesconsist of Ni(II)O nanocrystals imbedded in an amorphous matrix of Li₂O,Ni(III)O_(3/2) and M(A)O_(x/2). In embodiments where nanocrystals arepresent, it is believed that they fall within a narrow size range ofbetween about 3 nm to about 10 nm.

Another embodiment is to provide a method of preparing a counterelectrode layer for use in connection with an electrochromic devicecomprising a mixed oxide as described herein. The mixed oxide CEmaterial may generally be prepared and/or deposited according to themethods described in US2009/0057137, the disclosure of which is herebyincorporated by reference herein in its entirety.

In some embodiments, the CE material described herein is prepared byd.c. magnetron reactive sputter deposition, commonly used to coat windowglass with high performance optical coatings. In some embodiments, anelectrically conductive ceramic or metallic target is sputtered to ejecttarget material as a stream of atoms, into a low pressure, partialvacuum, partially ionized plasma or glow discharge. The atoms depositonto a substrate situated several centimeters from the target. Themethod is known as reactive sputter deposition because the metal atomsreact with the sputter gas, usually oxygen, as they travel to thesubstrate, or in some embodiments once they reach the substrate, to forman oxide.

Essentially, the target consists of a ceramic composite material, or asintered metal alloy, whose composition is formulated to match thelithium, nickel, and M composition of the counter electrode material inquestion. Oxygen is fed into the deposition process as a gas, diluted inargon to between about 10% and about 90%. Metal atoms are sputtered offof the sputter target by fast argon and oxygen ions that have beenaccelerated toward the target surface by an electrical field on theorder of several hundred volts. The target atoms sputtered into vacuumreact with oxygen on their way to the substrate or at the surface of thegrowing film. In some cases, intact metal oxide molecules are ejectedfrom the sputter target instead of metal atoms. The pressure in thesputter process vacuum vessel is about 2 to about 20 mTorr. The targetitself may be enriched with lithium relative to the desired filmcomposition to compensate for lithium loss to walls of the sputterchamber.

In some embodiments, the mixed oxide CE material is deposited on abuffer layer, the buffer layer (or some other intermediate layer) beingsituated between the CE layer and the ion conductor layer.

In some embodiments, additional lithium is inserted into the CE materialafter its deposition onto the ion conductor layer (or buffer orintermediate layer described above). The deposition of the lithium isachieved through one of wet chemical methods, sol-gel, chemical vapordeposition, physical vapor deposition, or reactive sputtering.

Typically the substrate 34 of the electrochromic device is comprised oftransparent glass or plastic such as, for example, acrylic, polystyrene,polycarbonate, allyl diglycol carbonate [CR39 available from PPGIndustries, Pittsburgh, Pa.], SAN [styrene acrylonitrile copolymer],poly(4-methyl-1-pentene), polyester, polyamide, etc. It is preferablefor the transparent substrate 34 to be either clear or tinted soda limeglass, preferably float glass. If plastic is employed, it is preferablyabrasion protected and barrier protected using a hard coat of, forexample, a silica/silicone anti-abrasion coating, a diamond-likeprotection coating or their like, such as is well known in the plasticglazing art. Generally, the substrates have a thickness in the range ofabout 0.01 mm to about 10 mm, and preferably in the range from about 0.1mm to 5 mm. However, any substrate of any thickness which will provide afunctioning electrochromic device may be employed.

It will be appreciated that the counter electrode layer 28 and theelectrochromic layer 30 may be reversed in the overall structure of FIG.1 . However, if the CE layer 28 and the EC layer 30 are reversed, thepolarity of the applied potential must be adjusted to ensure that thecorrect polarity for the layers is maintained.

The electrochromic devices described herein could be incorporated intoan insulated glazing unit, as known to those of ordinary skill in theart.

The electrochromic device described herein could be coupled withradiation sensors (e.g., visible and solar) and energy managementsystems to automatically control their transmission and reflection.

The electrochromic device as described herein may be powered with solarcells, thermoelectric sources, wind generators, etc., to make themself-sustaining. These may be also coupled into charge storage devicessuch as batteries, re-chargeable batteries, capacitors or other means.The charge storage devices could be utilized as automatic backup powersource when primary source of power is interrupted.

The electrochromic device may also be used as filters in displays ormonitors for reducing the ambient light intensity, e.g., sun glare thatis incident on the monitor or display surface. Thus, the device may beemployed to enhance the image quality of displays and monitors,particularly in well-lit conditions.

These electrochromic devices may also be used as displays having anadvantageously wide viewing area with a high contrast because nopolarizers are required as are in conventional liquid crystal displays.The device may also be used as eyewear or sunglasses.

Another exemplary embodiment provides a method of preparing a mixedoxide on a substrate.

Another exemplary embodiment provides a method of preparing anelectrochromic device comprising a counter electrode comprised of amixed oxide as described herein. A first conductive layer 26 isdeposited on substrate 34 by methods known in the art and in accordancewith the desired properties of a conductor layer as previouslymentioned.

An electrochromic layer 30 is then deposited on conductor layer 26through wet chemical methods, chemical vapor deposition and/or physicalvapor deposition (e.g. sol-gel, metallo-organic decomposition, laserablation, evaporation, e-beam assisted evaporation, sputtering,intermediate frequency reactive sputtering, RF sputtering, magneticsputtering, DC sputtering, PVD and CVD and the like). In preferredembodiments, the electrochromic layer 30 is deposited via intermediatefrequency reactive sputtering or DC sputtering techniques. In oneembodiment, the EC layer 30 is deposited on a heated first conductorlayer 26.

The deposited electrochromic layer 30 may be comprised of metal oxidesincluding titanium oxides, vanadium oxides, tungsten oxides, molybdenumoxides, or doped variants thereof. In a preferred embodiment, theelectrochromic layer 30 deposited is comprised of WO₃. In someembodiments, the deposited WO₃ may contain a stoichiometric excess ordeficiency of oxygen, depending on the deposition method and conditionschosen. In other embodiments, the WO₃ may be doped with an appropriatemetal or metallic compound.

An ion conductor layer 32 is then deposited on EC layer 30 through wetchemical methods, chemical vapor deposition and/or physical vapordeposition (e.g. sol-gel, metallo-organic decomposition, laser ablation,evaporation, e-beam assisted evaporation, sputtering, intermediatefrequency reactive sputtering, RF sputtering, magnetic sputtering, DCsputtering, PVD and CVD and the like). In a preferred embodiment, theion conductor layer is deposited via a sol gel method or reactivesputtering.

A counter electrode layer 28 comprised of a film of a mixed co-sputterdeposited lithium nickel metal oxide is then deposited on the IC layer32 (or an intermediate buffer layer as described above). The method ofdepositing this particular layer is disclosed herein.

A second conductive layer 24 is deposited on the lithiated CE layer 28by methods well known in the art and as described above in thedeposition of the first conductive layer 26.

As already mentioned, the position of the counter electrode layer 28 andthe electrochromic layer 30 may be reversed in the overall structurepresented in FIG. 1 . One skilled in the art would appreciate thatshould the layers be reversed, the method of manufacturing the devicedoes not change with regard to the steps that have to be performed togenerate each layer. One skilled in the art would appreciate that themethods utilized above to create a counter electrode comprised of aco-sputter deposited lithium nickel metal oxide material may be used todevelop a counter electrode for use in connection with anyelectrochromic device. That is, the methods used to develop the counterelectrode are not limited to use in the specific electrochromic devicediscussed herein. Moreover, the method of making the counter electrodediscussed above may also be used to deposit a counter electrode on anysurface, not merely ion conductor layers or other conductive layers.

Non-limiting examples pertaining to CE materials and the preparation ofCE materials are recited below. These examples are not intended to limitthe scope of the embodiments disclosed herein.

Non-limiting Example of Electrode preparation: Radio frequency (RF)magnetron sputtering was performed on an Angstrom EvoVac depositionsystem housed in a glove box under an argon atmosphere. Three-inchdiameter metal alloy targets, Ni—Zr (80-20 at. %) and Ni—W (80-20 at.%), were purchased from ACI Alloys, while a three-inch diameter ceramicLi₂O target (99.9%) supported on a molybdenum backing plate waspurchased from Plasmaterials, Inc. The gun powers for the metal alloytargets and ceramic target were 60 W and 45 W, respectively. Thetarget-substrate distance was 10 cm and remained constant throughout thestudy, and no additional heating was applied to substrate. The basepressure and total deposition pressure were 10-7 Torr and 2 mTorr,respectively. The Ar/O₂ gas mixture was fixed at 1/2 throughout thestudy. The fluorine-doped tin oxide (FTO) glass substrates werepurchased from Hartford Glass CO, Inc. (TEC 15, 1.5″×0.82″×2.3 mm). Thesubstrates were cleaned successively with soapy water, acetone,isopropanol and deionized water, and dried under flowing nitrogen gas.

Non-limiting Example of a Characterization Method: The crystalstructures of the resulting films were characterized on a Philips X-raydiffractometer Model PW1729 operated at 45 kV and 40 mA using CuK alpharadiation. Transmittance and reflectance measurements were performed ona Cary 6000i UV-vis-NIR spectrometer. Field emission scanning electronmicroscopy (FESEM) was done on a JEOL JSM-7000F Field Emission ScanningElectron Microscope with an EDAX Genesis EDS. X-ray photoelectronspectroscopy (XPS) was performed on a Kratos Axis HSi Ultra X-rayPhotoelectron Spectrometer using an Al Kα X-ray source operated at 14 kVand 10 mA. Transmission electron microscopy (TEM) was done on a FEITechnai G2 F20 TEM.

Non-limiting Example of Electrochromic Measurement: The measurementtechniques were reported previously. Briefly, electrochromic propertieswere measured in a liquid electrolyte half-cell where the electrolytewas 1 M lithium perchlorate (LiClO4) dissolved in propylene carbonate(PC). Cyclic voltammetry (CV) was carried out using a BioLogic VMP3multichannel potentiostat with a scan rate of 20 mV/s and a voltagerange of 1.7-4.2 V vs. Li/Li⁺. In-situ transmittance was measured usinga diode laser at 670 nm. Switching kinetics (i.e., coloration andbleaching) were measured under potential step cycling from 1.7 to 4.2 Vvs. Li/Li+, where each potential step was maintained for 2 min. Theswitching speed is defined as the time required achieving about 90% oftotal transmittance change within a potential step. All electrochemicalmeasurements were carried out under an argon atmosphere in a glove box.The samples were transferred from the sputtering chamber to testingcells without exposure to air or moisture.

EXAMPLE 1

Structural characterization results for the as-depositedLi_(2.34)NiZr_(0.28)O_(x) films prepared by RF magnetron sputtering areshown in FIG. 2 . Cross-sectional scanning electron microscopy (SEM)image (FIG. 2 a ) shows the film thickness is ca. 80 nm, which isthinner than reported nickel oxide-based anodic electrodes.

FIG. 2 b provides the X-ray diffraction (XRD) spectrum for theas-deposited Li_(2.34)NiZr_(0.28)O_(x) film. Only the (200) peak isobserved in the spectrum indicating that nickel oxide nanocrytalliteswere preferentially oriented along the <100> direction. Additionally,the diffraction angle (2θ=42.5°) was shifted towards a lower valuerelative to the face center cubic NiO indicating that the latticeconstant of the nickel oxide-based material is expanded due to thedoping of Zr and Li in the lattice.

High-resolution transmission electron microscopy (HRTEM) image is shownin FIG. 2 c . Nickel oxide nanocrytallites were believed to be imbeddedin an amorphous matrix, which is similar to the morphology observed inLi_(1.81)NiW_(0.21)O_(x) and porous WO₃ thin films. An amorphous matrixhas been shown to provide fast Li+ diffusion channels in nickeloxide-based anodic electrode materials. Importantly, the latticedistances of about 0.216 nm, about 0.217 nm and about 0.218 nm wereslightly larger than the standard d200 of cubic NiO, which is consistentwith the shift observed in the XRD spectrum. Inductively coupled plasmamass spectroscopy (ICP-MS) analysis confirms that the molar ratiobetween Li and Ni was about 2.3 (Li_(2.34)NiZr_(0.28)O_(x)).

EXAMPLE 2

X-ray absorption spectroscopy (XAS) was employed to investigate the Liand Zr co-doping effects on the electronic structure of nickel oxide.FIG. 3 presents a comparison of the Ni L-edge XAS for several nickeloxide-based thin films, corresponding to dipole transitions from Ni 2pto Ni 3d states, including both the 2p_(3/2) (LIII) and 2p_(1/2) (LII)spin-orbit final states. Due to the direct dipole transition from 2p to3d orbitals and the high resolution in the soft x-ray regime, L-edge XASof transition metals is sensitive not only to the valency of the metal,but also to the detailed energetics of the ligand-3d interactionsgoverned in particular by symmetry, as well as spin and hybridization.

Although rigorous treatment of all possible final states can becomplicated, the most salient features of the transition metal L-edgecan be captured by atomic calculations by the introduction of crystalfield effects. It is believed that the XAS spectrum for a NiO_(x) filmproduced by RF magnetron sputtering closely resembled previouslyreported data for nickel oxide films. Here, the NiO_(x) XAS spectrumrepresented transitions from Ni (2p⁶3d⁸) to Ni (2p⁵3d⁹), where the finalstate as probed by XAS was well described by atomic multipletcalculations for a single Ni²⁺ in an octahedral coordination (FIG. 3 ).Upon Li and Zr doping, the high-energy feature b (and e for the LIIIedge) was significantly enhanced. This was consistent with a formalincrease in the oxidation state of nickel. A similar enhancement in theintensities of features b and e was observed for a NiO_(x) film afterozone exposure (FIG. 4 ). Ozone treatment of as-deposited nickel oxidefilms was previously found to increase the amount of higher oxidationstate nickel species. It has been shown, however, that the spectralobservations cannot simply be ascribed by a linear combination of Ni²⁺and Ni³⁺ in an octahedral environment, since the increased hole statesupon doping is mainly localized on the oxygen orbitals of the NiO₆ unit.Thus, it has been concluded that Li and Zr have been successfully dopedinto the nickel oxide lattice and modified its electronic structure. Anickel oxide-based electrode containing Li/W additives was preparedutilizing identical sputter deposition conditions as used forLi_(2.34)NiZr_(0.28)O_(x). A chemical formula ofLi_(1.81)NiW_(0.21)O_(x) was determined by ICP-MS. The film thicknessand crystal structure of the Li_(1.81)NiW_(0.21)O_(x) film wereidentical to the Li_(2.34)NiZr_(0.28)O_(x) film (FIG. 5 ). The XASspectrum for Li_(1.81)NiW_(0.21)O_(x) demonstrated a similar co-dopingeffect as observed in Li_(2.34)NiZr_(0.28)O_(x) (FIG. 6 ).

EXAMPLE 3

Specific optical density=ln(% T _(b)/% T _(c))/thickness  Eq. (1)

Cyclic voltammetry and in-situ transmittance curves forLi_(2.34)NiZr_(0.28)O_(x) and Li_(1.81)NiW_(0.21)O_(x) thin filmelectrodes cycled in a 1 M LiClO₄ dissolved in propylene carbonate areshown in FIGS. 7 a and 7 b. The charge capacities (determined from theCVs) are 21.8 mC/cm² and 21.4 mC/cm² for the Li_(2.34)NiZr_(0.28)O_(x)and Li_(1.81)NiW_(0.21)O_(x) electrodes, respectively. The chargecapacities for Li_(2.34)NiZr_(0.28)O_(x) and Li_(1.81)NiW_(0.21)O_(x),it is believed, could be controlled (modified) easily by varying thefilm thickness. The in-situ optical modulation at about 670 nm for theLi_(2.34)NiZr_(0.28)O_(x) film was about 45% compared to about 35% forthe Li_(1.81)NiW_(0.21)O_(x) film. As determined by Eq. (1), the highspecific optical density (defined as the optical density per micrometer)for the Li_(2.34)NiZr_(0.28)O_(x) film (8.1 μm⁻¹) was comparable to thatof the state-of-the-art porous WO₃ film (9.0 μm⁻¹). Without wishing tobe bound by any particular theory, it is believed that a high specificoptical density enables a reduction in film thickness withoutcompromising optical contrast properties, therefore reducingmanufacturing costs. It should be noted that a thickerLi_(2.34)NiZr_(0.28)O_(x) film (about 200 nm) showed significantlyimproved optical modulation (about 72% at 670 nm) while maintaining anoptimal bleached state transparency (FIG. 8 ).

The coloration efficiencies of Li_(2.34)NiZr_(0.28)O_(x) andLi_(1.81)NiW_(0.21)O_(x) at 670 nm are ca. 33 cm²/C and ca. 31 cm²/C,respectively. Importantly, the bleached state ofLi_(2.34)NiZr_(0.28)O_(x) film was more transparent than that ofLi_(1.81)NiW_(0.21)O_(x) film. FIG. 7 c provides the UV-vis-NIR spectra(300-1500 nm) for the as-deposited, bleached and dark films. Overall,the as-deposited films showed similar optical characteristics exceptthat the Li_(2.34)NiZr_(0.28)O_(x) film had higher transmittanceespecially for irradiation wavelengths less than about 400 nm. Due toband gap and d-d transition absorptions, the transmittance of nickeloxide films typically decreased when the irradiation wavelength was lessthan 800 nm. However, the decrease did not occur in the bleached stateof the Li_(2.34)NiZr_(0.28)O_(x) film. A significantly larger contrastin the bleached-state transparency was observed for theLi_(2.34)NiZr_(0.28)O_(x) film in the UV-vis region relative to theLi_(1.81)NiW_(0.21)O_(x) film.

A relative determination of perceived light intensity with respect tothe human eye is necessary when a high level of transparency and nearcolorlessness is desired in the bleach-state of an electrochromicdevice. Therefore, utilizing the UV-vis-NIR data in FIG. 7 c , theCIE-defined L*a*b* color coordinates were calculated as detailed in theexperimental methods, where the three coordinates, L*a*b*, representedthe lightness of the color (L*), its position between red/magenta andgreen (a*, negative values indicate green and positive values indicatemagenta) and its position between yellow and blue (b*, negative valuesindicate blue and positive values indicate yellow). The b* values forthe bleached states of Li_(2.34)NiZr_(0.28)O_(x) andLi_(1.81)NiW_(0.21)O_(x) were estimated to be about 6.5 and about 12.6,respectively. A b* value below 8 was typically undetectable by the humaneye indicating that the bleached-state for Li_(2.34)NiZr_(0.28)O_(x) wasnearly colorless (no remnant yellow color, FIG. 7 d ). Furthermore, thebleached-state transmittance of Li_(2.34)NiZr_(0.28)O_(x) was highlyimproved in the near infrared region. This improved transparency acrossthe spectrum allowed for more efficient control of solar heat gain andnatural light harnessing.

EXAMPLE 4

Electrochromic processes in nickel oxide anodic electrodes are typicallyslower than in cathodic WO_(x) electrodes and, it is believed, impedethe overall switching kinetics of a layered electrochromic device.Wet-chemical synthesis routes have been employed to fabricate porousnickel oxide structures in order to reduce the switching time from onestate to another state. Improved optical switching (insertion andremoval of lithium) has also been observed in modified nickel oxidefilms synthesized using conventional sputter techniques. The normalizedin-situ transmittance changes under potential step cycling are shown inFIGS. 9 a and 9 b , for Li_(2.34)NiZr_(0.28)O_(x) andLi_(1.81)NiW_(0.21)O_(x), respectively. The switching speed was definedas the time required to achieve about 90% of transmittance change upon apotential step. In Li-ion electrolyte, the bleaching and colorationkinetics were both greatly improved for the Li_(2.34)NiZr_(0.28)O_(x)film, with bleaching (T_(b)) and coloration (T_(c)) times of about 18seconds and about 20 seconds, respectively. The T_(b) and T_(c) timesfor Li_(1.81)NiW_(0.21)O_(x) were 61 seconds and 31 seconds,respectively.

EXAMPLE 5

The interface between an electrochromic film and electrolyte plays acrucial role in facilitating the efficient insertion and removal oflithium. The surface composition of the nickel oxide-based electrodeswas probed with X-ray photoelectron spectroscopy (XPS) and O K-edge XAS.As shown in FIG. 10 , the XPS spectra for Li_(2.34)NiZr_(0.28)O_(x) andLi_(1.81)NiW_(0.21)O_(x) clearly demonstrated that the surfacecomposition of the modified nickel-oxide films depended on the metaladditives (Li/Zr vs. Li/W). High-resolution XPS identified every element(i.e., Li, Ni, W and O) present in the Li_(1.81)NiW_(0.21)O_(x) film.However, only Li and O were observed for the Li_(2.34)NiZr_(0.28)O_(x)film. This observation suggested that phase separation occurred duringthe deposition of the Li_(2.34)NiZr_(0.28)O_(x) film and a lithium richlayer (Li₂O and/or Li₂O₂) was generated on the surface of the film. OK-edge XAS spectra could, it is believed, directly reflect structuralinformation about electronic structure of O ions in the lithium richsurface layer. FIG. 11 a shows O K-edge XAS spectra for NiO_(x),Li_(2.34)NiZr_(0.28)O_(x) and Li_(1.81)NiW_(0.21)O_(x) materials. Thepre-edge feature at ca. 527 eV was believed to be attributed to thetransition of O is state to the unoccupied states (i.e., hole state)with p characteristics as a result of high oxidizing environment duringmaterial synthesis. A strong peak was found at ca. 533 eV for theLi_(2.34)NiZr_(0.28)O_(x) sample, which was believed to be a signaturefor lithium peroxide (i.e., Li₂O₂). This signature peak for lithiumperoxide was reduced for the Li_(1.81)NiW_(0.21)O_(x) film and wasconsistent with the XPS data where a lithium rich surface layer was notobserved for Li_(1.81)NiW_(0.21)O_(x). Based on the discussion above,FIG. 11 b was the proposed schematic representation ofLi_(2.34)NiZr_(0.28)O_(x) and Li_(1.81)NiW_(0.21)O_(x). To the best ofour knowledge, this is the first time that Li₂O₂ has been integratedwith an electrochromic electrode. It is believed that the formation of asurface Li₂O₂ layer facilitates the efficient diffusion of Li⁺ andaccounts for the superior switching kinetics observed inLi_(2.34)NiZr_(0.28)O_(x) relative to Li_(1.81)NiW_(0.21)O_(x).

EXAMPLE 6

The highly improved electrochromic performance in theLi_(2.34)NiZr_(0.28)O_(x) electrode is also associated with theuniqueness of the composition of the multicomponent films. FIGS. 12 and13 compare the in-situ optical modulation and switching kinetics ofNiZr_(x)O_(y) and Li_(x)NiO_(y). In general, without in-situ lithiation,the optical modulation for NiZr_(x)O_(y) would be exceedingly reducedand the bleached-state transparency would be significantly improved whenZr is present, presumable in the form of ZrO₂. These additional nickeloxide-based films showed that the improved depth of coloration andswitching kinetics were strongly reliant on the presence of ZrO₂ and alithium rich matrix (Li₂O and Li₂O₂) in Li_(2.34)NiZr_(0.28)O_(x).

EXAMPLE 7

The electrochromic mechanism of nickel oxide-based materials in Li-ionelectrolytes has been unclear due to the lack of detailed spectroscopicstudies. As shown in FIG. 14 a there was minimal difference between theNi L-edge XAS spectra for the Li_(2.34)NiZr_(0.28)O_(x) dark-state andas-deposited Li_(2.34)NiZr_(0.28)O_(x) films. These data were consistentwith the presence of high valence state Ni species (i.e., high holeconcentration). The Ni L-edge XAS spectrum for theLi_(2.34)NiZr_(0.28)O_(x) bleached state is shown in FIG. 14 a andclearly indicated significant decreases in the intensities of features band e relative to the dark-state. These results have been interpreted asa neutralization of the initial hole states by electrons from theexternal circuit leading to the bleached nickel oxide film. Thepenetration depth of soft X-rays (i.e., Ni L-edge) was limited to about5 nm. A XAS study of the bulk electronic structure of nickel oxideelectronic structure (i.e., Ni K-edge) is shown in FIG. 14 b . Thepre-edge feature at ca. 8332 eV was attributed to the transition from Niis to the hybridization state of Ni 3d and O 2p, and it was anindication of oxidation state for the target Ni atom. There are clearshifts in the pre-edge energy and pre-edge absorption between the darkand bleached samples, indicating the formal change of the Ni oxidationstate. Therefore, the electrochromic mechanism could be associated witha reversible transformation of formal Ni oxidation states, which wasclosely related to the well-known Bode mechanism. However, the observedchanges in Ni L-edge spectrum (FIG. 14 a ) indicated that the formalincrease of nickel oxidation state was not simply associated with achange from Ni²⁺ to Ni³⁺, but that the increased hole concentration wasmore localized on the neighboring oxygen, which then impacted the Nioxidation states through the Ni 3d-O 2p hybridization state. Anidentical Ni K-edge and Ni L-edge XAS study of Li_(1.81)NiW_(0.21)O_(x)confirmed that this mechanism was applicable for various nickeloxide-based anodic electrodes in Li-ion electrolytes (FIG. 15 ).

The CE materials described herein and the methods of depositing thesematerials allows for high-quality electrochromic films and tunablecontrol of material composition and structure. It is believed that theaddition of Li/Zr additives to nickel oxide was found to yield asuperior performing electrochromic material in terms of opticalmodulation, bleached-state transparency and switching kinetics relativeto the resulting nickel oxide material with Li/W additives. It isbelieved that the high specific optical density ofLi_(2.34)NiZr_(0.28)O_(x) allows for increased manufacturability. It isbelieved that the electrochromic effect in multi-component nickeloxide-based materials arises from the reversible formation of holestates that are localized on the neighboring oxygen orbitals.

EXAMPLE 8

FIG. 2 c shows an expanded NiO(II) nanocrystal lattice structure forLi_(2.34)NiZr_(0.28)O_(x) from High Resolution Cross SectionalTransmission Electron Microscopy (HRXTEM). The crystal structure of theNiO(II) nanocrystals is more open (lattice spacing=0.217 nm for NiO(200) plane) than for undoped Ni(II)O (0.209 nm). The micrograph alsoreveals that the nanocrystal size is approximately 5 nm.

EXAMPLE 9

FIG. 16 illustrates the increase in NiO(II) nanocrystal size with highernickel concentrations (Li0.0 Ni(II)_(0.5)Ni(III)_(0.5)W_(0.25)O_(2.25)compared to Li_(0.0)Ni(II)_(0.5)Ni(III)_(0.5)W_(0.2)O_(2.25) from X-raydiffraction. Essentially, it is believed that increasing the nickel totungsten ratio from about 1:0.33 to about 1:0.25, without lithium,increased the NiO(II) nanocrystal size from about 7 nm to about 9 nm.

Table 1 below illustrates how the amount of surface nickel varies withnano-crystal size. FIG. 1 depicts a nano-crystal with about equalamounts of core and surface material.

TABLE 1 Nano- Nano- Nano- crystal crystal Core crystal SurfaceNano-crystal Diameter, Volume, Volume, Surface/Core nm nm{circumflexover ( )}3 nm{circumflex over ( )}3 Ratio 2.1 1 6 5.39 2.7 3 9 2.92 3.48 15 1.77 4.6 27 28 1.01 5.8 62 44 0.70 7.3 138 69 0.50 9.1 300 110 0.3710.5 467 144 0.31 11.5 637 175 0.27 12.4 810 203 0.25

It is believed that a high proportion of nickel oxide at the surface ofthe nano-crystals is advantageous because the surface material iscompletely accessible to Li+ counter ions. At the surface, switchingbetween dark Ni(III) and bleached Ni(II) is likely to proceed bothreversibly and to stoichiometric completion (complete conversion).

The Examples discussed above are provided for purposes of illustrationand are not intended to be limiting. Still other embodiments andmodifications are also contemplated. While a number of exemplary aspectsand embodiments have been discussed above, those of skill in the artwill recognize certain modifications, permutations, additions and subcombinations thereof. It is therefore intended that the followingappended claims and claims hereafter introduced are interpreted toinclude all such modifications, permutations, additions andsub-combinations as are within their true spirit and scope.

The invention claimed is:
 1. An electrochromic device comprising: afirst electrode comprising one of an electrochromic layer or a counterelectrode layer, a second electrode comprising other of theelectrochromic layer or the counter electrode layer, a first conductivelayer, and a second conductive layer, the first and second electrodesbeing sandwiched between the first and second conductive layers,wherein: the counter electrode layer comprises at least one mixed oxidehaving a formula Li_(x)Ni(II)_(1-y)Ni(III)_(y)M(A)_(z)O_(a), where M isa metal other than Li and Ni; A is the most favorable oxidation state ofthe metal; x and z independently range from greater than 0 to about 10;y is greater than 0 and less than 1; and a ranges from about 0 to about10.
 2. The electrochromic device of claim 1, wherein M(A) is selectedfrom the group consisting of Al (III), Sc (III), Cr (III), Co (III), Y(III), Rh (III), In (III), La (III), Ce (III), Nd (III), and Sm (III).3. The electrochromic device of claim 2, wherein a is(1+0.5x+0.5y+1.5z).
 4. The electrochromic device of claim 1, wherein thecounter electrode layer has a dark state optical density of no more than20 μm⁻¹ at an optical wavelength of 450 nm.
 5. The electrochromic deviceof claim 1, wherein the counter electrode layer has a dark state opticaldensity of between 5 μm⁻¹ and 20 μm⁻¹ at an optical wavelength of 450nm.
 6. The electrochromic device of claim 1, wherein the counterelectrode layer has a dark state optical density of between 8 μm⁻¹ and12 μm⁻¹ at an optical wavelength of 450 nm.
 7. The electrochromic deviceof claim 1, wherein the counter electrode layer has a mixed electronicand ionic conductivity from 10⁻¹¹ Scm⁻¹ to 10⁻⁶ Scm⁻¹.
 8. Theelectrochromic device of claim 1, wherein the counter electrode layerhas a mixed electronic and ionic conductivity from 10⁻¹⁰ Scm⁻¹ to 10⁻⁶Scm⁻¹.
 9. The electrochromic device of claim 1, wherein the counterelectrode layer has a lithium charge capacity between 10 mC/cm² to 100mC/cm².
 10. The electrochromic device of claim 1, the counter electrodelayer has a refractive index from 1.7 to 2.5.
 11. The electrochromicdevice of claim 1, wherein: M is selected from the group consisting ofSi, Ti, Mn, Zr, Sn, Ce, Hf, Re, and Ir; and a is (1+0.5x+0.5y+2z). 12.The electrochromic device of claim 1, wherein the counter electrodelayer has a band gap energy from 2.5 eV to 6 eV.
 13. The electrochromicdevice of claim 1, wherein: M is selected from the group consisting ofV, Nb, Sb, Ta, and Pa; and a is (1 0.5x+0.5y+5z).
 14. The electrochromicdevice of claim 1, wherein M(A) is selected from the group consisting ofMg(II), Y(III), Si(IV), Ti(IV), Zr(IV), Hf(IV), Ir(IV), Nb(V), Ta(V),Mo(VI), and W(VI).
 15. The electrochromic device of claim 1, wherein: Mis selected from the group consisting of Cr, Se, Mo, Te, and W; and a is(1+0.5x+0.5y+3z).
 16. The electrochromic device of claim 1, wherein thethickness of the counter electrode layer is in a range from about 80 nmto about 500 nm.
 17. The electrochromic device of claim 1, wherein xranges from about 1.5 to about
 3. 18. The electrochromic device of claim1, wherein y ranges from about 0.4 to about 0.95.
 19. The electrochromicdevice of claim 1, wherein z ranges from about 0.15 to about
 1. 20. Theelectrochromic device of claim 1, wherein x ranges from about 1.81 toabout 2.5, y ranges from about 0.6 to about 0.9, and z ranges from about0.2 to about 0.5.